1. Field of the Invention
The present invention relates to a piezoelectric element having a multilayered structure, i.e., a multilayered piezoelectric element to be used as a piezoelectric actuator, an ultrasonic transducer and so on, and a method of manufacturing the multilayered piezoelectric element.
2. Description of a Related Art
A piezoelectric material represented by a material having a lead-based perovskite structure such as PZT (Pb (lead) zirconate titanate) provides a piezoelectric effect of expanding and contracting when applied with a voltage. A piezoelectric element having the property is utilized in various uses such as piezoelectric pumps, piezoelectric actuators and ultrasonic transducers. The basic structure of a piezoelectric element is a single-layer structure in which two electrodes are formed on both ends of one piezoelectric material. Accompanied with microfabrication and integration of piezoelectric elements with recent developments of MEMS (micro electro mechanical systems) related devices, multilayered piezoelectric elements each having plural piezoelectric materials and plural electrodes alternately stacked have been used.
FIG. 7 is a sectional view showing a structure of a conventional multilayered piezoelectric element. This piezoelectric element includes a multilayered structure having alternately stacked piezoelectric material layers 100 and internal electrode layers 110a and 101b, side electrodes 103a and 103b, an upper electrode 104 and a lower electrode 105. Insulating regions 102a and 102b are provided in the internal electrode layers 110a and 101b, respectively.
The side electrode 103a is connected to the internal electrode layers 110a and insulated from the internal electrode layers 101b by the insulating regions 102b. Further, the side electrode 103b is connected to the internal electrode layers 101b and insulated from the internal electrode layers 110a by the insulating regions 102a. Furthermore, the upper electrode layer 104 is connected to the side electrode 103a, and the lower electrode layer 105 is connected to the side electrode 103b. 
By forming the electrodes of the piezoelectric element in the above-mentioned manner, electrodes for applying electric fields to each of the piezoelectric material layers 100 are connected in parallel. Thereby, a capacitance between the electrodes of the multilayered structure as a whole becomes larger, and the rise in electrical impedance can be suppressed even when the size of the piezoelectric element is made smaller.
Further, instead of providing the insulating regions 102a and 102b in the internal electrode layers 110a and 101b as shown in FIG. 7, there is known a multilayered piezoelectric element in which each internal electrode layer is formed on an entire surface of respective one of the piezoelectric material layers and the internal electrode layer is insulated from either one of the side electrodes by forming an insulating film on an end surface of the internal electrode layer at a side surface of the multilayered structure.
However, in the multilayered piezoelectric element as shown in FIG. 7, there has been a problem that separation easily occurs in the connection region between the internal electrode layer and the side electrode. The reason is that, when the piezoelectric material layers expand and contract, the side electrodes are unable to follow the displacement of the piezoelectric material layers, and therefore, distortion is produced at the interface between the side electrode and the multilayered structure. Further, in the multilayered piezoelectric element having the insulating films formed on the side surfaces of the multilayered structure, the insulating films are apt to separate from the end surfaces of the internal electrodes for the same reason. Accordingly, there are problems that the reliability at the time of operation of piezoelectric element is low and the life of the element is short.